Compressor

ABSTRACT

A piston-type compressor has gaskets located between a cylinder blocks and front and rear housings mated to the cylinder blocks. The front and rear housings are made of magnesium alloy, and cylinder blocks are made of aluminum. The gaskets are constituted of resilient material and contain white carbon or a mixture of white carbon and black carbon to provide a superior electrical non-conductivity. The gaskets electrically isolate the housings and cylinder blocks so as to prevent a galvanic corrosion at surfaces where the two different metals of the compressor components are jointed.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a compressor, in particular, to a compressor having components, which are made of plural kinds of metallic materials.

[0002] Japanese Unexamined Patent Publication No.10-26077 discloses a compressor having cylinder blocks for accommodating pistons, and front and rear housings located at the front and rear ends of the cylinder blocks. The front and rear housings are clamped together through the cylinder blocks by bolts. In another words, through-holes are bored in the cylinder blocks and the bolts are through the through-holes and the ends are screwed on the rear housing so as to clamp the front and rear housings at both ends of the cylinder blocks.

[0003] The above-mentioned compressor has the front and rear housings made of aluminum. In order to reduce the weight of the assembled compressor, the housing can be made of magnesium alloy, the weight of which is lighter than if made of aluminum. Because the front and rear housings are relatively heavy parts in the compressor, lightening the weight of the housings is therefore effective in lightening the entire compressor weight.

[0004] However, if the compressor uses the magnesium alloy in the front and rear housings, there is a problem of corrosion in the area where the housings contacts the cylinder blocks, leading to a deterioration in the durability of the compressor. This is because the cylinder blocks are made of aluminum or iron, while the housings are made of magnesium alloy, a different metal. Each metal has a small inherent electrical potential. The inherent potential of magnesium is lower than that of aluminum. Therefore, at the contacting area between the housings of magnesium alloy and cylinder blocks of aluminum, there is an electrical potential difference, which causes a galvanic corrosion. The potential difference between the aluminum and magnesium alloy is greater than the potential difference between the aluminum and iron. The large potential difference tends to easily cause anodic corrosion in a low potential material such as the magnesium alloy. This corrosion is accelerated in particular equipment used in compressor, which are severe environments where the temperature and pressure are frequently varied. It is particularly likely that compressors of vehicle air conditioners suffer more serious corrosion, because they are usually exposed to water or salt, which further accelerate the corrosion. If severe corrosion of the housing develops, there is a possibility of leakage of refrigerant.

[0005] It is accordingly one object of the present invention to provide a lightweight and durable compressor having members made of low inherent electrical potential material, such as magnesium alloy, that can be mated to components having a different inherent electrical potential. A further object of the invention is to reduce galvanic corrosion in compressors of the type used in vehicle cooling systems and similar applications.

SUMMARY OF THE INVENTION

[0006] The present invention makes use of an insulator, between contacting area of the dissimilar metals, magnesium alloy and aluminum or iron, so as to prevent the galvanic corrosion. Particularly, an insulator containing white carbon has been found to provide superior electrical isolation of the dissimilar metallic components of the compressor and prevent the galvanic corrosion of the magnesium alloy, because the white carbon has high non-conductivity itself.

[0007] The compressor according to the invention has a first component made of first metallic material and a second component made of second metallic material, which has different inherent electrical potential from that of the first metallic material. An insulator containing white carbon is disposed between the mating areas of the first and second components, which, for example, may be consisted of magnesium alloy and aluminum or iron, and alloys thereof. In the preferred embodiment, magnesium alloy is, for example, applied to end housing whereas the cylinder block is made of aluminum or iron, or in alloy thereof. A more complete understanding the invention, and its features and advantages may be obtained from the following detailed description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The features of the present invention that are believed to be novel are set forth with particularity in the appended claims. The invention together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawing in which:

[0009]FIG. 1 is a cross-sectional view of a preferred embodiment of a compressor according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] An embodiment of a compressor incorporating the improved insulator of the present invention is shown in FIG. 1. This embodiment is a double-headed piston type compressor for a vehicle air conditioner of the type disclosed in U.S. Pat. No. 5,947,698, which corresponds to Japanese Unexamined Patent Publication No.10-26077.

[0011] Referring to FIG. 1, a compressor 101 has a pair of cylinder blocks 111, 112, which are coupled to each other at the mating ends of each cylinder block. A front housing 113 is coupled to the front end (left side of FIG. 1) of the cylinder block 111 with a valve plate 114 arranged in between. In the same manner, a rear housing 115 is coupled to the rear end (right side of FIG. 1) of the cylinder block 112 with another valve plate 114 arranged in between. In the embodiment, while each cylinder block is made of aluminum alloy, the front housing 113 and rear housing 115 are made of magnesium alloy. Because the weight of magnesium alloy is lighter than that of aluminum alloy, the entire weight of the compressor 101 can be lightened compared with the conventional compressor having aluminum housings.

[0012] Through-holes 117 for inserting bolts 119 extend through cylinder blocks 111, 112, so that the bolts 119 pass completely through the cylinder blocks 111, 112. In total, five the bolts 119 and five through-holes 117, of which all are not shown in the figure, are formed in the compressor 101.

[0013] The bolts 119 are made of iron and have male threaded ends 119 a. The male threaded ends 119 a go through bores in the front housing 113 and through-holes 117 to make with the threaded bores 120 in the rear housing 115. The diameters of the through-holes 117 are slightly greater than the diameters of the bolts 119 so as not to contact the bolts 119 with the front housing 113 and cylinder blocks 111,112. Accordingly, the front housing 113 and rear housing 115 are firmly clamped to the respective ends of cylinder blocks 111,112 when the bolts 119 are tightened, thereby forming a casing 102 of the compressor 101.

[0014] In the casing 102, a drive shaft 121 is rotatably supported by the center portion of each cylinder block 111,112 and the front housing 113. The drive shaft 121 will be connected and driven by power source such as an automotive engine through a clutch.

[0015] A crank chamber 127 is formed in the cylinder blocks 111,112. In the crank chamber 127, a swash plate 128 is fixed to the drive shaft 121 with a particular angle. Double-headed pistons 125 are reciprocatabley disposed in the cylinder bores 124. In each cylinder bore 124, compression chambers 126 are defined between each end of pistons 125 and respective valve plates 114. The pistons 125 engage the peripheral surface of the swash plate 128 through shoes 129.

[0016] When the drive shaft 121 rotates, the swash plate 128 also rotates. The rotating motion of the swash plate 128 is converted into the reciprocating motion of the pistons 125, with the piston displacement determined by the particular angle of the swash plate 128 relative to the drive shaft 121. The reciprocating motion of the pistons 125 compresses the refrigerant in the compression chambers 126.

[0017] A suction chamber 131 and discharge chamber 132 are formed in the both front housing 113 and rear housing 115.

[0018] The refrigerant is introduced into the suction chamber 131 from cooling circuit not shown in the figure connected to the compressor 101 by way of a suction conduit, via a suction valve mechanism 136. In the compression chamber 126, compressed refrigerant is discharged into the discharge chamber 132 through a respective discharge valve mechanism 137. From there, the compressed refrigerant enters an external cooling circuit through a discharge conduit.

[0019] According to the present embodiment, gaskets 140 are disposed between the mating faces between the front housing 113 and cylinder block 111, and between the rear housing 115 and cylinder block 112, respectively. The gaskets 140 are made of resilient material containing white carbon. Examples of a white carbon suitable for use in the gaskets 140 are silicic anhydride, silicic hydrate and synthetic silicate.

[0020] The gaskets 140 are formed from resilient material containing white carbon, which is usually applied to resilient material as reinforcer, and has inherently lower electrical conductivity compared to other reinforcers such as carbon black. Nevertheless, the gaskets 140 may contain both carbon black and white carbon, as well as white carbon only.

[0021] Test for corrosion resistance of magnesium alloy based on a salt spray test of JIS (Japanese Industrial Standard) Z2371, confirms that the white carbon content imparts a concomitant degree of corrosion resistance to the magnesium alloy in gaskets containing both white carbon and carbon black. In the preferred embodiment, all the reinforcer that is contained about 50% by weight of the resilient material is constituted of white carbon. Accordingly, the housings 113, 115, which are made of magnesium alloy, are electrically insulated from the cylinder blocks 111, 112, which are made of aluminum alloy by the gaskets 140.

[0022] As previously stated at points, where the magnesium alloy front housing 113 and rear housing 115 directly contact the aluminum cylinder blocks 111, 112 of aluminum, the galvanic corrosion occurs due to the inherent potential difference between aluminum and magnesium alloy being considerably higher than the inherent potential difference between aluminum and iron. The gaskets 140, electrically and physically isolate the magnesium alloy housings 113, 115 and aluminum cylinder blocks 111, 112. Therefore, the gaskets 140 prevent the galvanic corrosion at facing surfaces that otherwise would occur. The gaskets 140 perform both a sealing function and an anti-corrosion function.

[0023] As previously stated, the invention employs lightweight components to reduce the weight of the casing. The use of white carbon-containing isolating gaskets 140 between dissimilar metals prevents the galvanic corrosion that otherwise would result. This is especially distinct where the compressor 101 is exposed to severe environment such as water or salt that contributes factor to accelerate the corrosion when used in a vehicle air conditioner. Furthermore, because the gaskets 140 have two functions of seal and anti-corrosion, it does not need any additional parts.

[0024] Although only one embodiment of the present invention has been described herein, it should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the invention may be embodied in following form;

[0025] (A) In the above embodiment, the present invention is applied, by way of example, in a double-headed piston type compressor 101 of for a vehicle air conditioner. However, it may be embodied in the other types of compressors having different mechanism, such as a single-headed piston type compressor having a swash plate, or a so-called a variable displacement compressor that varies the angle of inclination of the swash plate. Furthermore, the present invention may be embodied in so-called scroll type compressor that has a movable scroll rotating in relation to a stationary scroll, or the other compressors for other than air conditioner for vehicle.

[0026] (B) In the above embodiment, the compressor 101 has the front housing 113 and rear housing 115 made of magnesium alloy. However, the magnesium alloy can be embodied in other members of the casing 102, such as entire cylinder blocks 111, 112 or the one of them. Of course, it is recommended that the bores of through-holes be slightly greater than the outer diameters of the bolts as not to contact the side surface of bolts with the inner bore surface of the cylinder blocks 111,112. This avoids inadvertent galvanic corrosion between steel bolts and magnesium alloy casing parts.

[0027] Furthermore, when one of the cylinder blocks 111, 112 is made of magnesium alloy and another is made of aluminum, a gasket located between the two cylinder blocks may contain white carbon. Such gasket can also prevent galvanic corrosion therebetween.

[0028] (C) In the above embodiment, the white carbon constitutes about 50% by weight of the resilient material. However, a mixture of white carbon and carbon black may be used in the gaskets. In this case, the compound ratio of white carbon and carbon black can be determined in view of a preferred corrosion resistance. For example, to ensure the required electric non-conductance, the compound ratio of the carbon black may be 10% or less by weight, preferably, 5% or less by weight with the white carbon constituent presenting in greater amounts of about 40% to about 45% by weight of the resilient material. 

What is claimed is:
 1. A compressor comprising: a first component member made of first metallic material; a second component member made of second metallic material which has different inherent electrical potential from that of the first metallic material; and a resilient insulating member disposed between the first component member and the second component member so as to electrically isolate the component members from one another, wherein the resilient insulating member is constituted a resilient material containing white carbon.
 2. The compressor according to claim 1, wherein the second metallic material has lower inherent electrical potential than that of the first metallic material.
 3. The compressor according to claim 1, wherein the first metallic material is aluminum or an aluminum alloy.
 4. The compressor according to claim 1, wherein the second metallic material is magnesium or a magnesium alloy.
 5. The compressor according to claim 1, wherein the compressor is a piston type compressor, and the first component member is a cylinder block, which accommodates a piston inside.
 6. The compressor according to claim 1, wherein the compressor is a piston type compressor, the second component member is a housing mated to a cylinder block.
 7. The compressor according to claim 6, wherein at least one of a suction chamber and a discharge chamber is provided in the housing.
 8. The compressor according to claim 1, wherein the white carbon is selected from the group constituting of silicic anhydride, silicic hydrate, synthetic silicate and a mixture thereof.
 9. The compressor according to claim 1, wherein white carbon is present in an amount of about 50% by weight of the resilient material.
 10. The compressor according to claim 1, wherein the resilient insulating member contains carbon black.
 11. The compressor according to claim 10, wherein carbon black is present in an amount of about 10% by weight or less of the resilient material.
 12. The compressor according to claim 10, wherein carbon black is present in an amount of about 5% by weight or less of the resilient material. 